5B Mechanical Philosophy. 



heat, are curious, and highly intercstino^. He 

 ceems to have demonstrated that the different 

 prismatic colours have different grades of tempe- 

 rature; that radiant heat, as well as light, is not 

 only refrangible, but also subject to the laws of 

 dispersion, arising from its different refrangibility; 

 that those rays of light which have the greatest 

 illumimiting power are the yellow, and those 

 which have the greatest heating power the Ted; 

 and, of course, that, contrary to the general belief, 

 the maximum of illumination, and the maximum 

 of heat, do not coincide.'^ 



ASTRONOMY. 



Though this subject is mentioned last, it holds a 

 very conspicuous place among those branches of 

 mechanical philosophy which have received great 

 accessions of discovery and improvement during the 

 century in question. At the beginning of this period 

 the Principia of the immortal Newton had given a 

 new face to astronomical science. Much had been 

 done by his predecessors, and especially by the sa- 

 gacious Kepler, to prepare the way for his grand 

 discoveries; but it was reserved for this luminary 

 of the first magnitude to shed a degree of light on 

 the laws of our planetary system, which has served 

 to guide every exertion, and point out the way to 

 all progress which has since been made. It was 

 he who first applied the simple principle of gravi- 

 tation to account for the movements of the celes- 

 tial bodies; who laid down the laws of this great 

 and all pervading attraction; and thence, bv the 

 assistance of a sublime geometry, deduced the re- 

 >Jolutions of the planetary orbs, both primary and 



IV See Transaction* of the Royal Society for 1800, 



I 



